An electrically-conductive paste is well known. The electrically-conductive paste includes matrix material made of a thermosetting resin and electrically-conductive particles dispersed in the matrix material. The electrically-conductive particles are metallic particles, for example. An adhesive sheet made of a resin material is sandwiched between printed wiring boards so as to bond the printed wiring boards to each other, for example. Lands on the printed wiring boards are opposed to each other through a through bore formed in the adhesive sheet. The through bore is filled with the electrically-conductive paste. The electrically-conductive paste is hardened or cured by heating. The adhesive sheet bonds the printed wiring boards to each other. An electric connection is established between the lands opposed to each other.
It is proposed to bond a build-up layer to a core substrate for establishment of a so-called build-up substrate. It is required to establish a stable electrical connection between a land on the core substrate and a land on the build-up layer when the build-up layer is bonded to the core substrate. The aforementioned electrically-conductive paste cannot provide a reliable bonding between the build-up layer and the core substrate.